Seismographic prospecting



y 1943- A. c. WINTERHALTER 2,325,157

Filed Aug. 5, 1939 AMPLIFIER [vhf/E55" fi rcal Wzl z ria/zer y i w Patented July 27, 1943 SEISMOGRAPHIC PROSPECTING Alfred C. Winterhalter, Beaumont, Tex., assignor to Sun Oil Company, Philadelphia, Pa., a corporation of New Jersey Application August 3,1939, Serial No. 288,156

Claims. This invention relates to seismographic prospecting, and particularly to improved means for recording the instant an explosion takes place.

In seismographic work it is essential that the instant of explosion be determined on the record to a high degree of accuracy, and it is customary, therefore, to record the instant at which the firing circuit is disrupted by the explosion. Diificulties are sometimes encountered, particularly when th instant of break is transmitted by radio to a remote recording station in securing a sharp indication of the instant whem the break occurred. Usually both the make and break of the firing circuit are noted, and in the event that the break is not sharply indicated, the time of break may be determined with mor or less accuracy from the less significant instant when the circuit is made, using the knowledge of the approximate delay between the make of the circuit and the break occasioned by the explosion.

In accordance with the present invention, the break only is recorded, without any interference due to the making of the firing circuit. A sharp indication of the instant of break may thus be transmitted either by wire or by radio to the re-. cording apparatus. Specifically, in accordance with the invention, the break is used to produce a voltage adapted to-fire a gas filled tube to produce an impulse arranged to control the operation of a radio transmitter.

The broad and subsidiary objects of the invention will become apparent from the following description, read in conjunction with the accompanying drawing, in which:

Figure 1 is a wiring diagram showing the improved circuit applied to firing by means of a blasting machine; and

Figure 2 is a. partial similar diagram illustrating the modifications necessary in the event that firing is accomplished by the use of a battery.

Referring first to Figure .1, there is illustrated at 2 a triode, which may be interposed between the oscillator Al and the amplifier 6 of a conven- ;iona1 radio transmitting circuit, or which may 1e one of the amplifying tubes of the amplifier Wstem. The amplifier, in any event, feeds the ;ransmitting antenna 8 from which a signal is lent to a remote recording apparatus. A leak :ircuit of the grid ll] of the tube 2 comprises a radio frequency choke l2 and series resistances It and it, the two resistances together forming he proper grid leak for normal operation and he resistance l6 being of proper value for control y the gas tube circuit, as hereafter described.

At t it there is indicated a gas triode of the coldcathode starter-anode type. This tube may, for example, be of the OA4-G type and may comprise the anode 20, cathode 24 and starter-anode 26. The operation of this type of tube is well known and involves the initiation of a discharge.

between the cathode and starter-anode, which discharge effects a discharge betweenthe cathode and anode if the anode potential is surficiently high and the starter-anode current exceeds some predetermined value. For example, in a typical case, volts between the starter-anode and cathode will produce a discharge between them. If, then, the anode voltage with respect to cathode is about volts, 2. current of 25 microamperes in the starter-anode circuit will cause a discharge between the cathode and anode. On the other hand, if breakdown of the starter-anode circuit has not occurred, the anode breakdown will not occur until a minimum potential of about 225 volts between the anode and cathode is exceeded.

Connected to the junction point of the resistances l4 and i6 is a battery 22 having 2. voltage of, for example, 180 volts. A switch 23 is interposed between the positive side of this battery and the anode 20, this switch serving to interrupt the discharge at a proper time.

The cathode 24 may be connected directly to ground and the cathode of the tube 2.

The starter-anode 26 is connected through a current limiting resistance 28 to thepositive pole of the blasting machine, indicated at 32. Shunted across the blasting machine are the stabilizing resistance 30, which may have a high value such as one megohm, a safety switch 38, which is closed except at the time of firing, and the leads 34 connected to the igniting filament 36 of the detonator of the charge 31. The leads 34 should be well insulated to prevent leakage and maintain high the resistance across the blasting machine upon breaking of the igniting filament.

In the operation of this arrangement, following the proper placing of the charge and the rendering of the radio transmitter operative to transmit a continuous wave, the safety switch 38 is opened to remove the short circuit from the firing leads and the switch 23 is closed to impose the potential of the battery 22 upon the anode. The potential thus imposed is insuificient to cause discharge in the absence of discharge at the starter-anode, and consequently no current flows through the resistance l6 except the normal grid current of proper amount to provide the bias for the amplifying tube 2.

When the blasting machine 32 is operated, its

terminal voltage is impressed upon the starteranode and the leads to filament 36, however, is the internal impedance of the blasting machine is sufilciently high so that accompanying the relatively heavy current which flows to the igniting filament there is a terminal voltage considerably less than the 90 volts required to initiate starter-anode discharge.

At the instant the filament is disrupted by the filament 36. The of low resistance and the explosion, however, the terminal voltage of v the blasting machine rises instantly to its open circuit value, the high resistance offering no substantial load. This open circuit potential is generally about 150 volts, quite suflicient to initiate the starter-anode discharge. Furthermore, the voltage is sumciently high to cause to fiow through the starter anode and its series resistance 28 a current of suflicient value to initiate anode discharge under the 180 volts provided by the battery 22. As soon as discharge is initiated, the potential drop between the anode and cathode reaches a value substantially constant at '70 volts, and hence the difierence voltage between the voltage of the battery and this potential drop is imposed across the resistance l6, biasing the tube 2 to cut-ofi. Since there is no large impedance in the circuit capable of producing any appreciable delay, it will be evident that for all practical purposes the cut-off of the tube 2 occurs at the instant of the firing of the shot. Thus this instant may be transmitted to secure a record of extremely high accuracy.

the radio. The value of the resistance l6 must,

be such as to limit the anode current to asafe value to prevent damage to the tube l8. The resistance 28 likewise prevents damage which might be caused by excessive starter-anode current. The leak resistor 30 must be provided to avoid accidental tube discharges which may occur in the event that the starter-anode is free.

While a cold cathode gas tube has been specifically described, it will be evident that hot cathode types may be equally well used. The grid or starter-anode control may be either positive or negative, depending upon the type of tube, suitable biasing being provided if necessary. In general, gas rather than vapor tubes are to be recommended because of the possible instability and accidental discharge of vapor types.

In Figure 2 there is illustrated the modification' necessary to adapt the circuit to battery firing. The tube It! may be of the same type as that of Figure 1, for example an OA4-G. The firing battery is indicated at Ml, While at 42 there is indicated the internal resistance of the battery or, in the event that that is insufficient, an auxiliary resistance adapted to insure that, when the circuit is closed for firing by means of the switch 43, the terminal voltage is insuflieient to cause a starter-anode discharge. In case a battery is used, the voltage necessary to produce starter-anode discharge would be considerably in excess of the voltage desired for firing the detonator. Accordingly, m bias battery 44 is introduced adapted to maintain on the starter-anode a voltage, insuffici nt to cause its discharge upon closure of th firing circuit, but suflicient to produce discharge when added to the open circuit voltage of the battery t ll, which is imposed across the resistance 30 as soon as the filament is disrupted by the explosion. In all respects except those noted, the circuit is, of course, the same as that of Figure 1.

What I claim and desire to protect by Letters Patent is:

1. In combination, a firing circuit for an explosive charge, current supplying means for said circuit, signal transmitting means, and means for controlling the transmitting means to transmit a signal upon disruption of the firing circuit by explosion of a charge, said last named means comprising a grid controlled electronic tube of relay type having its grid input circuit connected across said current supplying means in shunt with said firing circuit so that upon disruption of the firing circuit the potential of the grid is raised sufficiently to cause discharge of said tube.

2. In combination, a firing circuit for an explosive charge, current supplying means for said circuit, signal transmitting means, and means for controlling the transmitting means to transmit a signal upon disruption of the firing circuit by explosion of a charge, said last named means comprising a grid controlled electronic tube of relay type having its grid connected to said firing circuit in a manner to render it operative upon disruption of the firing circuit.

3. In combination, a firing circuit for an ex plosive charge, current supplying means for said circuit, signal transmitting means, means for controlling the transmitting means to transmit a signal upon disruption of the firing circuit by explosion of a charge which simultaneously causes an electrical change in the firing circuit, said last named means comprising a grid controlled electronic tube of relay type arranged to discharge by rise of grid potential, and connections between the tube and firing circuit whereby said electrical change efi'ects a rise of grid potential to the discharge point upon disruption of the firing circuit.

4. In combination, a firing circuit for an explosive charge, current supplying means for said circuit, signal transmitting means, means for controlling the transmitting means to transmit a signal upon disruption of the firing circuit by explosion of a charge which simultaneously causes an increase of voltage across the firing circuit, said last named means comprising an electronic tube of. relay type, and connections between the tube and the firing circuit whereby it is arranged to discharge in response to said increase of voltage across the firing circuit upon disruption thereof.

5. In combination, a firing circuit for an explosive charge, current supplying means for said circuit, signal transmitting means comprising a thermionic vacuum tube having a grid, and means for controlling the transmitting means to transmit a signal upon disruption of the firing circuit by explosion of a charge which simultaneously causes an electrical change in the firing circuit, said last named means comprising an electronic tube of relay type, and connections between the last mentioned tube and the firing circuit whereby it is arranged to discharge upon the disruption of the firing circuit, and connections through which such discharge changes the bias on said grid.

ALFRED C. WINTERHALTER. 

